Mesoscopic study on the effect of CFRP layers on the mechanical properties of coal circular-columns

In order to study the effect of CFRP layers on the mechanical properties of coal cylinders. A discrete-continuous coupled meso-mechanical numerical model of CFRP passively confined coal cylinders was developed using a three-dimensional FLAC-PFC coupling method. The validity of the model was verified with experimental data of 0-2 layers of CFRP passively confined coal cylinders. On this basis, studies of the influence of 3-7 layers on mechanical properties and energy evolution of CFRP confined coal cylinders was carried out. The results show that the yield limit and the peak of the coal cylinders gradually coincide with the increase of CFRP layers, showing a state of yielding or failure without warning. With the increase of CFRP layers, the increment in the peak strength of coal cylinders first increases and then decreases. A function is obtained to characterize the evolution of the peak strength increment of CFRP confined coal cylinders under different layers. The increment in the peak strain shows a behavior of first increasing and then decreasing, and then increasing and decreasing again. When the elastic strain energy is constant, the axial strain of the coal cylinders has no correlation with CFRP layers, but its peak strain and ultimate strain both increase with the increase of CFRP layers. The dissipative energy conversion ratio at peak point increases first and then decreases with the increase of CFRP layers. A function is established to characterize the evolution of the dissipative energy conversion ratio of CFRP confined coal cylinders with different layers. The ductility characteristics of stress-strain curves, peak strength increment, peak strain increment, dissipative energy conversion ratio and total energy increment of coal cylinders are considered comprehensively, and taking into account the principles of economic cost and winding level, the three layers are determined as the optimal winding layers for CFRP confined coal circular-columns.